1. Field of the Invention
The present invention relates generally to chains, including but not limited to those used to transmit torque between sprocket wheels, and more particularly to an adjustable segmented chain, having a plurality of substantially similar modular links, or pairs of links, capable of interconnecting to form a closed loop chain, such as is commonly used to transmit pedal or motor generated power to one or more drive axles, wheels, or accessories in bicycles, motorcycles, pedal boats, automobiles, household appliances (such as washing machines and driers), and in industrial, military, space, and extreme environment applications. The chain of the present invention may also have applications as a tow chain, as an anchor chain, as a chain used for jewelry bracelets and necklaces, for strap handles of suitcases or purses, as clothing belts, etc.
2. Description of Related Art
Chains are commonly used to transmit torque between rotating devices: for example, bicycle chains transmit torque between sprocket wheels. Conventional bicycle chains, as have been used for one hundred years, consist of a closed oval or circular loop made of a plurality of multi-pan metal modules or links, narrow links alternating and hinged together with wide ones, each link being fitted at its interior to receive the teeth of sprocket wheels, and each link interleaving end-to-end with its adjoining neighbor, joined together by a shared metal pin set perpendicular to the length of the joined links and which pin acts as a fulcrum or axle allowing pivoting between each of the chain's pairs of links to occur substantially in one single plane around that axle. The chains for bicycles which use a derailleur shifting arrangement must allow adjoining links to pivot two directions to accommodate primary and reverse curves (around the derailleur) in one plane; also, for the chain to be derailed from one sprocket wheel to another in the same concentric cluster, a certain small amount of lateral slip or pivot is allowed to occur at the pivoting connection between chain links.
Chains must provide tensile strength to withstand and transmit torque. The perpendicular structure of each link which meshes with the teeth of sprocket wheels must provide both impact and tensile strength. In addition, chain links must pivot with respect to one another to permit the chain to conform and bend either direction in one plane around sprocket wheels without excessive friction and wear. To provide the required strength, conventional chains are made of metal. To permit pivoting, the links of conventional chains are hinged with and connected by metal pins which function as axles, relative to which are attached and turn the two separated side pieces of one module before and those of another behind.
Like the spacing of their sidewalls, conventional chain links are alternatively wide and narrow. The pin is riveted or splayed at each end to sandwich, and prevent the escape of various skewered metal parts: e.g. a more widely spaced side piece from the left module but which extends some distance above, below and beyond the pin connection; then, rubbing against it, a side piece from the right module and its extension; then a wide washer; then the other side piece from the right module, including its extensions; then the other side piece from the (more wide-sided) left module, including extensions; then the rivet or splayed other end of the pin. The spacing "washer" at the middle of each such pin sandwich holds the left and right sidewalls of each module separate from each other to permit entry of sprocket teeth but allows friction to occur between the two left sides of adjoining modules and the two corresponding fight sides. There is friction also between the washer ends and the module sidewalls which touch it, and between the pin and all the components it penetrates. By its bulk this washer also protects the modules' interconnecting metal hinge pins from the wear they would experience if they were struck repeatedly and directly by the teeth as sprocket wheel and chain engaged or if the pedal or motor power applied between sprocket tooth and chain were carried directly by and to the narrow pin in contact with the working edges of sprocket wheel teeth across the direction of their work. Lubricants such as oil typically are used to reduce friction at the points where module side walls and washers turn against one another, the teeth, and pins.
Conventional chain designs, as described above and in common use to transmit power to bicycle drive wheels, have changed little for decades. U.S. Pat. No. 1,130,582 J. M. Dodge, Mar. 2, 1915, is not fundamentally different from the more recent patents reviewed, which reflect mere modifications and improvements. For example, U.S. Pat. No. 4,596,539 K. Yamasaki, May 7, 1985, to facilitate the chain being derailed from one sprocket wheel to another, introduces cutouts or hollows on the inward-facing marginal edges of the wider links. U.S. Pat. No. 4,960,403 M. Nagano, Jul. 28, 1989, proposes deforming the metal of the wider links outward to accomplish the same purpose. U.S. Pat. No. 5,226,857 T. Ono, May 13, 1992, blends the improvements of the Yamasaki and Nagano patents and asserts that the metal deformation and hollowing need occur on one side of the chain only, since the shifting problem noted is significant primarily when the chain goes from a smaller to a larger sprocket wheel (and not vice versa) and since a bicycle's rear sprocket cluster typically has more narrowly spaced and more stages than does its front sprocket cluster.
U.S. Pat. No. 5,288,278 M. Nagano, Dec. 30, 1991, modifies the standard bicycle chain link by adding a flexion limiting device intended to prevent chain tangling during bumpy mountain bike rides. This patent too is limited to conventional chains which employ alternating narrower and wider links rotatably coupled by pins.
All of the conventional chains reviewed tend to be made of steel or other metal. They tend not to slip against the wheels they turn, as belts may against smooth pulleys, because they make a strong mechanical connection, link against sprocket, perpendicular to the direction of chain movement. However, chains so designed have several drawbacks, the relative importance of which in the bicycle application are roughly as follows: (1) they are relative heavy; (2) they rust; (3) they consist of multiple pans; (4) they are complex to manufacture, (5) they present much surface area to dirt and contamination; (6) they require repeated applications of messy, dirt-collecting oil for lubrication; (7) they are hindered by friction between links during rotation; (8) they wear out and/or stretch; (9) they are noisy; and (10) they can be difficult to install and replace.
As a result of the foregoing drawbacks, conventional chains tend to be used only in applications where power transmission is paramount, giving way to belts in other applications. In addition, conventional chains leave something to be desired, at least for certain applications, in other respects. (11) Their high mass and inertia make them somewhat difficult to accelerate and decelerate. (12) They are not particularly aerodynamic. (13) They are wider than is strictly functional, due to their alternatingly wide and narrow sidewalls. (14) They require a specially designed link pin where breakage, if any, tends to occur. (15) Like a baseball bat they are inflexible, and thus they cannot store and release power like a golf club. (16) Their length is not easily varied.
The present invention is a different kind of chain, as strong and powerful as needed, yet designed to minimize each of the disfunctionalities associated with conventional type chains. (1) The modules and chain of the present invention are light weight, being formed typically of injection molded plastics the specific gravities of which may be a fraction (often less than one-sixth) that of their conventional metal counterparts. Sprocket clusters too can be made of lightweight plastic once chains are. This further increases the weight savings. The dimensions of the modules also can be reduced to further reduce weight, if appropriate in terms of the balance of other characteristics desired. In the cycling world, light weight is particularly important for racing and hill climbing applications.
(2) Because it is made of plastic the present invention does not rust. Rust is a major problem for the chains of many amateur cyclists.
(3) The present design involves many fewer parts than the conventional one. Each standard module is of one piece only (typically consisting of two injection-molded pieces bonded or otherwise joined to one another during assembly). Some, but not all, embodiments also require a second type of module for closing and unclosing the loop, which again may be formed of only two pieces removably connected. (4) Fewer parts should mean simpler manufacturing and assembly processes. (5) Unibody modules present a minimal surface area to dirt and contamination.
(6) A number of the plastics which could be used, such as nylon with fiberglass, are or can be considered to be, self-lubricating; thus, the use of oil lubricants can be reduced or eliminated, in turn reducing mess and the adhesion of dirt. Anti-static properties can be given the plastic also to minimize dust and dirt collection, and the rotating joint between modules can itself be shaped so that it will tend to expel contaminants. (7) The present design reduces friction, not only by reducing dirt and contaminants. With the present design, unlike the conventional one, there is little or no friction between the sidewalls of different links when they rotate with respect to one another, nor between sidewalls and the "washer" or other bulk surrounding the pin. Thus a reduced surface area bears friction when the links pivot.
(8) Reducing dirt and friction reduces chain wear. The wear and/or stretch associated with the present invention also will depend on the characteristics of the plastics and additives (e.g. carbon fiber or glass) used, with tradeoffs perhaps necessary at this stage in plastics engineering between strength (impact and/or tensile), on the one hand, and optimal weight and lubricity characteristics, on the other. (9) Plastic links are relatively quiet. (10) The chain of the present invention is relatively simple to install and replace. In a preferred embodiment, it requires the use of no tools to assemble and no tools, or a cutting tool only, to disassemble. It is feasible to replace individual links, not just the entire chain. And it is unnecessary to remove the bicycle's wheels to remove or install the chain.
(11) The chain of the present invention has low mass and inertia. Thus a bicycle using it will be relatively easy to pedal. (12) The links of this chain have smooth, rounded edges and are identical to one another in shape and size, not angular and alternatingly wide and narrow like the conventional chain; hence the chain is aerodynamic, and (13) its overall width may be reduced, if desired, thus permitting more tightly clustered, hence more, sprockets. (14) This chain requires no specially designed, breakage-prone link pin, thus it can be engineered without points more liable to break than the others. (15) The present invention can be made of flexible materials, if desired. In conjunction with oval sprocket wheels or the like, such chain flexibility could be useful to store and release pedal power so as to smooth or otherwise optimize the power curve. (16) The present invention permits ready changes in chain length and tension since the number of links to be used is variable and can be modified from time to time with relative ease.